1. Field
A linear compressor and a linear motor are disclosed herein.
2. Background
In general, compressors are mechanical apparatuses that compress and raise a pressure of air, a refrigerant, or various other operating gases, by receiving power from power generating apparatuses, such as electric motors or turbines, and may be widely used in electric home appliances, such as refrigerators and air conditioners, and in most industries. Compressors are roughly classified into reciprocating compressors, in which a compression space into which and from which an operating gas, such as a refrigerant, is suctioned and discharged, is formed between a piston and a cylinder, and in which the piston is linearly reciprocated inside of the cylinder to compress the working gas; rotary compressors, in which a compression space into and from which an operating gas, such as a refrigerant, is suctioned and discharged, is formed between an eccentrically-rotated roller and a cylinder, and in which the roller is eccentrically rotated along an inner wall of the cylinder to compress the working gas; and a scroll compressor, in which a compression space into and from which an operating gas, such as a refrigerant, is suctioned and discharged, is formed between an orbiting scroll and a fixed scroll, and in which the orbiting scroll is rotated with respect the fixed scroll to compress the working gas.
Recently, among reciprocating compressors, linear compressors that linearly reciprocate pistons, have simple structures, can improve compression efficiency, and are not subject to mechanical loss resulting from motion conversion, have been developed in many forms. Generally, a linear compressor is configured to suction and compress a refrigerant while a piston is linearly reciprocated within a cylinder by a linear motor in a sealed shell, and discharge the compressed refrigerant.
FIG. 1A is a schematic diagram of a linear motor for a linear compressor according to the conventional art. Referring to FIG. 1A, a conventional linear motor 1 may include an outer stator 10, an inner stator 20, and a permanent magnet 30 movable between the outer stator 10 and the inner stator 20. The outer stator 10 may surround a bobbin 16 having a coil 15 wound thereon.
The outer stator 10 may include a first core 11 that extends in a moving direction of the permanent magnet 30, that is, a direction substantially parallel to an axial direction; a plurality of second cores 12 that extends from both ends of the first core 11 in a direction substantially perpendicular to the axial direction; and a plurality of magnetic poles 13 that extends from each of the plurality of second cores 12, respectively, in directions such that they extend closer to each other. The plurality of magnetic poles 13 has sectional areas in the axial direction that become progressively smaller as they extend closer to each other.
Recently, technology providing a more linear compressor has been developed. Manufacturing of a linear motor may be considered a technique for making a linear compressor more compact.
In conventional linear motors, to reduce an outer diameter Dm of the linear motor while maintaining a total cross-sectional area of the coil wound on the bobbin, a reduction of the outer diameter Dm of the linear motor by reducing widths of the plurality of magnetic poles may be considered.
FIG. 1B is a graph illustrating width of a magnetic pole and a motor force constant when the width of a magnetic pole is reduced. Referring to FIG. 1B, the motor force constant denotes a magnitude of back electromotive force induced in the coil when the permanent magnet is moved by a predetermined distance from an outer end portion of one magnetic pole of the outer stator to an outer end portion of the other magnetic pole within a range of a movable trajectory X. As the motor force constant within the range of the movable trajectory becomes greater, and as a slope becomes constant, efficiency and output of the motor improves.
When a width w of the magnetic pole 13 is reduced to w′, saturation becomes stronger at inner end portions 14 of the plurality of magnetic poles 13 which are within the range of the movable trajectory X of the permanent magnet 30, and the motor force constant becomes smaller. The inner end portions 14 of the plurality of magnetic poles 13 are ends of portions adjacent to each other at each of the magnetic poles.
Also, the motor force constant rapidly decreases at outer end portions (an end portion of a portion adjacent to the second core 12 at each of the magnetic poles) of the plurality of magnetic poles 13. Thus, a slope of the motor force constant becomes larger and a decrease in efficiency and output of the motor may occur.